HAZARD AND OPERABILITY STUDY (HAZOP) SUMMARY

gTET, the Organic Rankine Cycle (ORC) generator manufacturer engaged Simplified Safety Solutions

Australia (SSSA) to conduct a structured and systematic examination of the whole geothermal plant

process and operation to identify and evaluate problems that may present risks to personnel or

equipment. The HAZOP facilitator was an independent consultant from SSSA to review the fail-safe

mechanism from a neutral view point and was selected by gTET from the LGIS/ Peak employee

referral. The main goal was to review the design and pick up any design and/or engineering issues

that may otherwise not have been found.

The study was conducted at the Local Government House (LGIS office) on 9th November, 2016. The

HAZOP team was comprised of Winton Shire Council representative, gTET senior management team,

Marley Flow representative, and the geothermal project manager from LGIS/ Peak. The study was

facilitated by a Principal Consultant from Simplified Safety Solutions Australia.

The HAZOP facilitator was provided with the technical details and performance specification of the

ORC generator, cooling tower and integration interface (eg piping, control system, electrical

connection) approximately four weeks prior to the date. The HAZOP study was arranged in a seminar

where the design (ORC generator, cooling tower and interface) were displayed in large posters and

the facilitator presented his safety concerns as identified during his review. The HAZOP team

proactively participated during the HAZOP study – both in terms of raising safety concern and

providing solution. During HAZOP, the geothermal power station was broken down into four nodes

to facilitate identification of potential issues. For all the potential issues raised at each node, the

HAZOP study found most of the fail-safe issues were already considered by the manufacturer and

the remaining few were not. For all the issues that were yet to be considered in the plant design, the

manufacturers (gTET and Marley) and LGIS project manager updated the design to integrate all the

issues raised in the HAZOP study. Four nodes of the geothermal power station are-

1. Heating Circuit –Geologically heated water from Town Bore No 4 is piped into a heat exchanger where it heats the R152a fluid causing it to evaporate. (marked in ash colour)

2. ORC Circuit –The heat exchange causes the R152a to evaporate and expand. This gas then turns a turbine before being cooled and condensed. It is then pumped (as a fluid) back to the heating side for evaporation. (marked in sky blue colour)

3. Cooling Circuit –Water from an adjacent cooling tower is pumped to the condenser to revert the R152a back to a liquid form. (marked in violet colour)

4. Electrical System –Electricity generated by the turbine is used to power auxiliary motors or pumps with the excess exported to the electricity grid. (marked in green colour)

Figure 1: Geothermal plant node sections for HAZOP study

To ensure safe operations and effective monitoring, the geothermal plant is fitted with a Supervisory

Control and Data Acquisition (SCADA) system, alarms and various components to monitor, identify,

alert and automatically take response measures whenever any issue occurs. The SCADA system will

also keep historic records of any issues that occurs. The overall SCADA system got several fail-safe

mechanisms. The ultimate fail-safe mechanism would be triggered when the “critical

communication” of the SCADA system is lost, it would automatically shut down the plant. The plant

would need to re-start manually after resolving the technical issue in such situation. Below are the

safety issues that were considered at each node’s operation:

1. Heating Circuit:

At this node, the plant is fitted with the following components that will serve respective safety

measures:

a. Pressure relief valves (PRV), pressure and flow transmitters to prevent pump overspeed due

to the high flow, prevent any high or low pressure, reverse flow or no flow that might cause

an operational failure and alarm any issues (including pipe blockage) that might affect

performance of the plant.

b. To prevent damage to heat exchanger, the system is fitted with temperature transmitters to

automatically monitor incoming water temperatures and stop the operation when

temperature reaches 98oC.

c. The plant’s monitoring system prevents any unwanted contamination by automatically

detecting R152a, any seepage/leaks and automatically shut down the plant depending on

error. Flashing umber lights and alarms are also installed to warn of any leaks, including

refrigerants. Detailed response in the event of refrigerant leaks are included in the operating

manual.

d. Onsite, there will be a dedicated safety zone and “DANGER: no smoking, no naked flame”

signs will be installed across the perimeter.

2. ORC Circuit

In the ORC Circuit, R152a detectors, PRV, pressure, flow and temperature transmitter will continue

their role as in node 1. Using the above components together with the turbine trip, the SCADA

system will prevent and alert any evaporation or condensation issues that might affect or damage

the system. In order to prevent the working fluid from condensing at incorrect temperatures, a

system check will be required following any addition of fluid to the system.

3. Cooling Circuit

In addition to components fitted to protect the system from leaks, blockage, condensation,

evaporation and any flow, pressure or temperature related issues as in the previous nodes, the

cooling circuit is also fitted with fan motor sensors to monitor and alert cooling tower fans’

performance. Depending on the issue identified, the SCADA system will automatically take

protective response measures, alert/alarm the issue and/or shut down the entire system if required.

Detailed emergency response of any possible failure will be included in the operating manual.

4. Electrical System

To prevent equipment damage due to Arcing/Arc flash from high voltage/current, the geothermal

plant is fitted with circuit breaks, active front end and MICOM P142 relays to manage ORC output

and ensure safe operations. The geothermal plant is also fitted with an energy storage system in

case of no power event, grid failure or any electrical protection device trip.